Hydrostatic Thickness

Use functions from metpy.calc as well as pint’s unit support to perform calculations.

The code below uses example data from our test suite to calculate the hydrostatic thickness between the surface and 500-hPa level for the provided sounding data.

import pandas as pd

from metpy.calc import (mixing_ratio_from_relative_humidity, relative_humidity_from_dewpoint,
                        thickness_hydrostatic)
from metpy.cbook import get_test_data
from metpy.units import units

Upper air data can be obtained using the siphon package, but for this example we will use some of MetPy’s sample data.

# Set column names
col_names = ['pressure', 'height', 'temperature', 'dewpoint', 'direction', 'speed']

# Read in test data using col_names
df = pd.read_fwf(get_test_data('jan20_sounding.txt', as_file_obj=False),
                 skiprows=5, usecols=[0, 1, 2, 3, 6, 7], names=col_names)

Drop any rows with all NaN values for T, Td, winds

df = df.dropna(subset=('temperature', 'dewpoint', 'direction', 'speed'
                       ), how='all').reset_index(drop=True)

Isolate pressure, temperature, and dewpoint and add units

p = df['pressure'].values * units.hPa
T = df['temperature'].values * units.degC
Td = df['dewpoint'].values * units.degC

Calculate the relative humidity to compute the mixing ratio

rh = relative_humidity_from_dewpoint(T, Td)
mixrat = mixing_ratio_from_relative_humidity(p, T, rh)

Calculate the thickness from the pressure, temperature, and mixing ratio for the layer from the surface pressure to 500-hPa

print(thickness_hydrostatic(p, T, mixing_ratio=mixrat, depth=p[0] - 500 * units.hPa))

5332.474521891784 meter

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